Definition
The angle between the chord line of a propeller blade and the plane of rotation, measured at a specific point along the blade (typically the 75 percent radius station). It determines how much air each blade slices and pushes rearward with every revolution.
Plain English
How steeply the propeller blades are tilted into the oncoming air. A flatter tilt takes a small bite of air; a steeper tilt takes a bigger bite.
Context Anchor
Encountered when studying controllable-pitch and constant-speed propellers, especially how the propeller control changes engine speed and aircraft performance.
Derivation
From the Latin propellere, 'to drive forward.' The 'blade angle' simply names the geometric tilt of each blade. The term is descriptive: it is literally the angle at which the propeller's blade is set.
Why Pilots Care
Correct blade angle produces the right amount of thrust without over-speeding or lugging the engine.
Analogy
Think of it like the pitch of a paddle in water. Hold the paddle nearly flat and you slice through with little resistance and little push. Tilt it more and each stroke moves more water but takes more effort.
Grounding Statement
Picture the blade set flatter for an easier, faster spin, and steeper for a bigger bite of air that loads the engine more.
Intuition Check
Do not confuse propeller blade angle with the pilot’s pitch attitude or the airplane’s nose position. Here, “angle” means the measured setting of the propeller blade itself relative to the circle it spins in.
Example Sentence 1
As airspeed increased in the climb, the governor increased blade angle to maintain the selected 2,400 rpm.
Example Sentence 2
In cruise flight the governor increased blade angle to keep RPM steady as airspeed rose.